The present invention relates in general to the glass decorating technology of screen printing radiation curable compositions onto glass substrates, e.g., glassware, in various predetermined patterns and registrations, which compositions are environmentally safe by virtue of being free of toxic heavy metals and volatile organic compounds ("VOC"). Still more particularly, the present invention is directed to an apparatus and method for decorative screen printing various glassware with such a composition curable using ultraviolet radiation ("UV") and the like in preexisting screen printing decorating equipment modified in accordance with the present invention.
In the glassware decorating industry there exists the desire to apply multiple registered layers which frequently overlap one another for decorative and other purposes. To overprint one layer with another, the art has recognized the use of hot melt ceramic printing inks which solidify sufficiently between printing stations to enable overprinting with the next layer of the printing ink without the adverse consequences of streaking and the like of the previously applied layer. However, it is known in addition to this process being relatively slow, that these printing inks contain undesirable toxic heavy metals and volatile organic compounds such as solvents which have been made the subject of increased environmental regulation. Consequently, the glassware decorating industry has sought to replace these ceramic printing inks containing VOC's and toxic heavy metals with pigmented UV curable pigmented compositions which are environmentally safe. See UV Inks Move Into the Light, David Aynessazian, American Ink Maker, pp. 43-45, July 1994.
To this end, there is known from U.S. patent application Ser. Nos. 199,414 and 199,415 now U.S. Pat. Nos. 5,571,359 and 5,487,927 respectively, both filed on Feb. 22, 1994 and assigned to the same assignee of the present application, pigmented UV curable compositions which are free of VOC's and toxic heavy metals suitable for decorating glass substrates, thereby rendering them environmentally safe. Notwithstanding the existence of these novel compositions, known screen printing decorating equipment available for applying multiple overlapping layers in registration with one another have been designed to accommodate the use of hot melt ceramic printing inks which enable their solidification between adjacent printing stations.
Because of the significant costs involved in the design and purchase of new screen printing decorating equipment, it would be desirable to retrofit existing equipment for use with these novel UV curable compositions. Unfortunately, the current equipment are not designed to accommodate a UV curing workstation subsequent to the next screen printing station in order to cure the composition after it has been applied. This problem becomes especially acute with multiple color printing processes in which multiple separate color images must be sequentially applied, often in registration with one another, by separate printing screens requiring a curing step after each image application.
Accordingly, there is an unsolved need for a screen printing decorating equipment which has been adapted to accommodate a UV curing workstation and method therefore to accommodate the printing of multiple registered images with UV curable compositions which are environmentally safe by being free of toxic heavy metals and VOC's.